Control device for hydraulically operated tappet valves of internal combustion engines

ABSTRACT

In an internal combustion engine, each intake and exhaust valve is operated by an actuating piston, which, in turn, is reciprocated by hydraulic liquid admitted under pressure to, and withdrawn from said piston intermittently by means of a solenoid valve.

United States Patent 1191 1111 3,727,595 Links 145] Apr. 17, 1973 1CONTROL DEVICE FOR [58] Field of Search ..123/90.1 1, 90.12,HYDRAULICALLY OPERATED 123/9015 TAPPET VALVES OF INTERNAL V COMBUSTIONENGINES 1561 References CM [75] Inventor: Heinz Links,Stuttgart.GermanyUMTED STATES PATENTS 73 I 3,220,392 11 1965 Cummins ..123/90.12 X l Ilgnce 2?" Swmart 3,548,793 12/1970 Richardson", 123/90.11 x ermmy2,392,207 1/1946 Weiss 6181 ..123/90.11 x 22] Fi Aug 3 7 3,209,73710/1965 Omotehara et a1 .1.. ]23/9()112 [21 1 APPL NQ-I 68,362 PrimaryExaminer-Al Lawrence Smith I Att0rneyEdwin E. Greigg 30 Forei A li t PriD l 1 pp 57 ABSTRACT 'A .30, 1969 G 13:57 16, 1969 2; :3 2: 912. 1 an iP gz engme F i Feb, 12, 1970 Germany ..P 20 06 304.1 aust V f y an F b14 970 G 4 1n turn, 15 recxprocated by hydrauhc 11qu1d admltted e ermdny..P 20 06 844.4

I under pressure to, and wlthdrawn from sa1d plston 1n- Feb. 25, 1970Germany ..P 20 08 668.4 eminent! b means of a Solenoid valve Mar. 5,1970 Gcrma n'yum'. ..P 20 10 291.4 y y 1 1 Claim, 16 Drawing Figures[52] U.S. Cl ..123/90.12, 123/90.l5 [51] Int. Cl ..F0ll 9/02' PATENTEU 171973 SHEET 02 HF 10 PATENTEB APR 1 71973 SHEET 05 0F 10 III 5 3PATENTEB APR 1 71973 SHEET 08 0F 10 PATENTEDAPRWW 3,727,595

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SHEET 10 [1F 10 PATENTEB APR 1 H973 CONTROL DEVICE FOR HYDRAULICALLYOPERATED TAPPET VALVES OF INTERNAL COMBUSTION ENGINES BACKGROUND OF THEINVENTION valve in a closed position.

In a known control device for tappet valves according to the aforenotedtype (such as described in Swiss Pat. No. 245,788),'the liquid isintermittently pressurized by means'of a cam-driven piston. The meteringof the pressurized liquid is effected by a separately driven controlmember. According to anotherknown valve control device of the aforenotedtype (such as described in German Pat. No. 858,329), again, the liquidis pressurized by a cam-driven pump piston. In the pressure conduitthere is disposed a check valve, while for permitting a closing motionof the engine valve, a return conduit controlled by the pump piston, isconnected with a chamber of lower pressure.

In control devices of the aforenoted type; the elasticity of the fluidin the system is a determining factor for the limits of possibleapplications. Due to the relatively long fluid conduits, a large fluidvolume is present which, dependent upon the rpm and thus the throttleeffect, causes a shift in the motion pattern between the pump piston andthe engine valve. Such an occurrence results in an interference with thepredetermined closing and opening moments of the valve. Furthermore,temperature variations also have an adverse effect, since they causechanges in the volume of the control liquid. Also, due to the elasticityof the fluid conduits, pressure oscillations may occur which may causenatural resonances of the valves thus resulting in an interruption ofthe connection between pump piston and cam or valve stem and actuatingpiston. The harmful result of such an occurrence is that the closing motion of the valves may not be controlled, a factor which may also leadto valve leakage. In addition to the aforenoted disadvantages, more orless for each type of engine a particular structure of cam, pump,piston, etc. is required, so that an overall standardization and massproduction with the inherent beneficial savings in the manufacture ofthe entire control system for the intake and exhaust valves hasheretofore not been possible.

OBJECT AND SUMMARY OF THE INVENTION It is an object of the invention toprovide an improved device for the control of hydraulically operatedAccordingly, the tappet valve stem is in engagement with an actuatingpiston which is intermittently displaced by the liquid delivered underpressure to the control device by a delivery pump in a continuousmanner. Contact between the actuating piston and the pressurized liquidin the control device is intermittently established by a periodicallyenergized solenoid valve. The latter includes a movable valve memberwhich, dependent upon the energized or the de-energized condition of thevalve solenoid, may assume two positions. In one position it admits thepressurized liquid to said actuating piston, while in the other positionit causes withdrawal of said liquid therefrom. When communicationbetween the actuating piston and the continuously delivered pressurizedliquid exists, the actuating piston, urged by the pressurized liquid,executes its working stroke whereby the tappet valve is opened.

The invention will be better understood, as well as further objects andadvantages of the invention will become more apparent, from the ensuingdetailed specification of several exemplary embodiments taken inconjunction with the drawing.

BRIEF DESCRIPTION OF THE DRAWING FIG. 1 is an axial sectional view of anembodiment of the invention including a schematic representation of gthe associated liquid circuit;

FIG. 2 is an axial sectional view of a further embodiment of theinvention;

FIG. 3 is a valve lift diagram pertaining to the operation of theembodiments according to FIGS. 1 or 2;

FIG. 4 is a sectional view of another embodiment of the inventionincluding a schematic representation of an associated liquid circuit;

FIG. 5 is a fragmentary sectional view of the same embodiment showingsome components in an alternate position;

FIG. 6 is a sectional view of still another embodiment of the inventionincluding a schematic representation of an associated liquid circuit; 7

FIG. 7 is a fragmentary sectional view of the same embodiment showingsome components in an alternate position;

FIG. 8 is a sectional view of a further embodiment of the inventionincluding a schematic representation of an associated liquid circuit;

FIG. 9 is a fragmentary sectional view of the same embodiment showingsome components in an alternate position;

FIG. 10 is a sectional view of a further embodiment of the inventionincluding a schematic representation of an associated, electronicallycontrolled liquid cir- 'cuit;

FIG. 10a is a block diagram of an electronic control apparatusassociated with the embodiment shown in FIG. 10;

FIG. 11 is a diagram of valve lift curves illustrating the operation ofthe embodiment according to FIG. 10;

FIG. 11 is a sectional view of another embodiment of the inventionincluding schematic representations of associated fluid circuits; 7 l

FIG. 13 is a diagram of valve lift curves illustrating the operation ofthe embodiment according to FIG. 12; FIG. 14 is a sectional view ofstill another embodiment of the invention including a diagrammaticrepresentation of associated liquid circuits; and

FIG. 15 is a diagram of valve lift curves illustrating the operation ofthe embodiment according to FIG. 14.

DESCRIPTION OF THE EMBODIMENT SHOWN IN FIG. 1

FIG. 1 illustrates the invention in its simplest form. In

a partially shown cylinder head 1 of an internal combustion engine thereoperates a tappet valve 2 having a valve stem 3 axially slidably guidedby a bearing sleeve 4 secured in the wall of the cylinder head 1. Theouter end of the valve stem 3 carries a spring seat disc 5. Between theupper face of the cylinder head 1 and the spring seat disc 5 there isdisposed in a preloaded condition a valve closing spring 6. To thecylinder head 1 there is secured a housing bracket 7 containing asolenoid valve generally indicated at 8 and an actuating piston 9. Thelatter is axially displaceably guided in a fluid-tight manner in abushing 10 threadedly secured to the bracket 7. During the valvemovement, the lower terminal face of the actuating piston 9 is urgedinto contact with the valve stem 3. The actuating piston 9 projects'into a chamber 11 which is provided in the bushing 10 and whichreceives a spring 12 urging the actuating piston 9 in the closingdirection of the tappet valve 2.

A delivery pump 14 draws liquid from a tank 13 and 1 delivers it under apressure of, for example 100 kg/cm through a pressure conduit 15 towardsthe solenoid valve 8. From the conduit 15 there extends, downstream ofthe pump 14, a return conduit 16 in which there is disposed a pressurecontrol valve 17 and which terminates in the tank 13.

In the housing bracket 7 supporting the solenoid valve 8, the liquidfirst flows into a pressure chamber 19 which is connected with a controlchamber 21 by means of a bore 20 serving as a supply channel. The mouthof the bore 20 at the control chamber 21 serves as a valve seat for asphere 22 which is movably disposed in the control chamber 21. From thecontrol chamber 21 there extends a bore 23 to the chamber 11. From thecontrol chamber 21 there also extends a bore 24 which is in continuouscommunication with the tank 13 through a discharge channel 25 and areturn conduit 26. The 'mouth of the bore 24 at the control chamber 21serves as a valve seat for the valve sphere 22. An armature 28, having apin-like extension 28' in contact with the sphere 22, is slidablydisposed in the bore 24 and urges, under the action of a spring 27, thesphere 22 into a position in which it closes the bore 20.

The control chamber 21, the bore 24 and the armature 28 are contained ina valve support sleeve 29 which is inserted in the housing bracket 7 andwhich is held in position by a flange of the housing 30 of theelectromagnet forming part of the solenoid 8. The electromagnet chamberaccommodating the spring 27 and the bore 20 immediately upstream of thesolenoid valve, are interconnected by means of a channel 31 so that inboth I aforenoted spaces identical pressures prevail. Further, thediameter of the cylindrical surface of armature 28 sliding in the bore24 in a fluid-tight manner, -is identical to the diameter of both seatsfor the sphere 22. Thus, as long as the sphere 22 is in a position shownin FIG. 1, the force derived from the pressure prevailing in bore 20 andexerted on the sphere in the opening direction, is identical to theforce of the pressurized liquid exerted on the sphere by the armature 28in the closing direction. Spring 27 aids the latter force so that thesphere 22 is, as a net result of the opposing forces, urged against themouth or valve seat provided about the bore 20.

As soon as the coil 33 of the electromagnet is energized, for example,by an electronic control device, the force of the spring 27 is overcomeby the magnetic force and the armature 28 is displaced towards the left.The pressurized liquid thus may flow through bore 20, pressing thesphere 22 against its other, opposite seat formed about the opening ofbore 24. As a result,

sphere 22 closes the bore 24 so that the liquid admitted under pressurethrough the bore 23 may flow into the chamber 11, after displacing theactuating piston 9. This results in the opening of the tappet valve 2.

' As soon as the solenoid 33 is deenergized, the spring 27 returns thearmature 28 and the sphere 22 into their initial position in which thebore 20 is again closed. As the bore 24 is opened by the returningsphere 22, the liquid may flow from the chamber 11 through the bore 24,the channel 25 and the return conduit 26 to the liquid tank 13 allowingthe actuating piston 9 to return. This, in turn, causes the tappet valve2 to assume its closed position.

DESCRIPTION OF THE EMBODIMENT SHOWN IN FIG. 2

In the embodiment shown in FIG. 2, the admission of liquid to theactuating piston 9 is effected by a servooperated control means. Thisembodiment finds application particularly in large internal combustionengines, where greater forces are needed to open the engine valves. Inthis structure the hydraulic servo circuit is controlled by a solenoidvalve of the type and in the manner as described in connection with theembodiment depicted in FIG. 1. The liquid admitted through the conduit15 flows through a channel 37 into an annular groove 38 which is formedin the wall of a bore 39. From the annular groove 38 there extend thepressure chamber 19 and the bore 20. In the bore 39 there operates acontrol plunger 40 which is in engagement with an axially aligned piston50.

Controlled by the solenoid valve 8 as described in i connection withFIG. 1, the pressurized liquid flows from bore 20 to control chamber 21,bore 23 and then through a channel 41 to a lower radial face of piston50. Under the effect of this liquid pressure, the piston 50 and thus thecontrol plunger 40 are displaced against the force of a spring 42disposed in bore 39. In the cylindrical face of the control plunger 40there is provided a circumferential annular groove 43 which is incontinuous communication with the annular groove 38. The portion of thebore 39 accommodating the spring 42 is'connected through a channel 44with the return conduit 26 terminating in the liquid tank 13.

In the bore 39 there is formed an annular groove 45 which is incommunication through a channel 46 with one side of a bore 47 in whichthere is reciprocably arranged an actuating piston 48. In the controlplunger 40 there are provided radial bores 49 which, in the position ofthe control plunger 40 as shown in FIG. 2, connect the bore 47 with thedischarge channel 44.

As soon as the solenoid of the electromagnet is energized, thepressurized liquid displaces the piston 50 and the control plunger 40against the force of the return spring 42 whereby the annular groove 43shifts into alignment with the annular groove 45 while, at the sametime, the bores 49 hydraulically separate from the annular groove 45. Inthis manner the liquid present under pressure in the annular groove 38may flow through the annular grooves 43 and 45 to the radial face of theactuating piston 48 and thereby effect an opening of the tappet valve.

As soon as the solenoid of the electromagnet is deenergized, the controlplunger 40 is returned by the spring 42 into its initial position inwhich the annular grooves 45 and 43 are separated from one another,whereas the radial bores 49 are re-connected with the annulargroove 45.Upon this occurrence, the pressurized liquid present above the actuatingpiston 48 may flow from the bore 47 through the annular groove 45 to theliquid tank 13. As a result, the tappet valve closes.

In the afore-described embodiments the work pistons 9 and 48 affectdirectly the stem 3 of the tappet valve 2. It is to be understood thatbetween piston and valve stem there may be provided any other forcetransmitting means, such as a rocker arm, or the like.

EXAMINATION OF VALVE LIFT CURVES OBTAINABLE BY THE EMBODIMENTS ACCORDINGTO FIGS. 1 AND 2 The diagram shown in FIG. 3 particularly wellillustrates the advantages of the afore-described embodiments. In thediagram the stroke s of the tappet valve is shown as a function. of theangular position of the cam shaft. The stroke s designates thestructurally possible maximum stroke of the tappet valve. The valve liftcurve I pertains to a tappet valve operated conventionally by the cam ofa cam shaft. The relatively flat initial portion of the ascent andrelatively flat terminal portion of the descent of the curve is causedby the fact that the flanks of a cam, for starting and terminating theforce transmission to the push rod, must not be steep. A transition intoa steeper range may occur only when the stroke is already under way. Asa result, at the beginning and at the end of this valve lift curve thereare points in which the velocity of the tappet valve is close to zero.The effective open period x flow passage section (hereinafter designatedan open time area) is the areabelow the curve I.

The lift curves II, III and IV represent the stroke ofa tappet valveoperated by means of a device according to the afore-describedembodiments of the invention. These curves all have a relatively steepcourse since the switching time of the electromagnet is extremely short.Thus, the slope of these curves depends exclusively from. flowresistances and refill'periods. Since the open ing time of the solenoidvalve always remains the same, whereas the aforenoted effects changewith the rpm (i.e. with the available length of time), to each rpm therecorresponds a different curve. Thus, curves II, III and IV correspond tothree different rpms. In the stroke portions s s and s s the dampeningbecomes effective. At points s and s a substantial change of the curveslope begins. While at s towards the end of the opening stroke, themotion of the actuating piston is dampened, during the return motionthereof, i.e. during the closing motion of the tappet valve (on theright side of the diagram), the setting motion is damped from s;, on.

As it may be well observed from FIG. 3, the area under the curves II,III and IV is substantially larger than that under the curve 1,resulting in the advantages set forth earlier.

DESCRIPTION OF THE EMBODIMENT ACCORDING TO FIGS; 4 AND 5 Turning now toFIGS. 4 and 5, in a partially shown cylinder head la of an internalcombustion engine there operates a tappet valve 2a having a valve stem3a axially slidably guided by a bearing sleeve 4a secured in the wall ofthe cylinder head la. The outer end of the valve stem 3a carries aspring seat disc 5a. Between the upper face of the cylinder head 1a andthe spring seat disc 5a there is disposed in a preloaded condition avalve closing spring 6a. To the cylinder head la there is secured ahousing bracket 7a containing a solenoid valve generally indicated at 8aand an actuating piston 9a. The latter is axially displaceably guided ina fluidtight manner in a bushing 10a secured to the bracket 7a. Duringthe valve movement, the lower terminal face of the actuating piston 9ais urged into contact with the valve stem 3a. The upper end of actuatingpiston 9a projects into a chamber 11a.

A delivery pump 14a draws liquid through a suction conduit 12a from atank 13a and delivers it under a pressure of, for example kg/cm througha pressure conduit towards the solenoid valve 8a. From the conduit 15athere extends, downstream of -the pump 14a, a return conduit 16a inwhich there is disposed a pressure control valve 17a and whichterminates in the tank 13a.

From conduit 151; there extend conduits 18a which lead to the controldevices of the other engine valves and which carry liquid under pressuredelivered by the same pump 14a.

In the bracket housing 7o supporting the solenoid valve 8a, the liquidfirst flows through a supply channel 19a which is connected with acontrol chamber 21a by means of a bore 20a serving also as a supplychannel. The mouth of the bore 20a at the control chamber 21a serves asa valve seat for a sphere 22a which is movably disposed in the controlchamber 21a. From the. control chamber 210 there extends a bore 230 tothe chamber 110. From the control chamber 21a there also extends a bore240 which is in continuous communication with the suction conduit 12athrough discharge channels 25a and 26a and a return conduit 26a. Themouth of the bore 24a at the control chamber 21a serves as a valve seatfor the valve sphere 220. An armature 28a, having a pin-like extension28a in contact with the sphere 22a, is slidably disposed in the bore 24aand urges, under the action of aspring 27a, the sphere 220 into aposition in which it closes the bore 20a.

The control chamber 21a, the bore 24a and the ar mature 28a arecontained in a valve support sleeve 29a which is inserted in the housingbracket 7a and which is held in position by a flange of the housing 30a.of the electromagnetic forming part of the solenoid 8a. Theelectromagnet chamber accommodating the spring 27a and the bore 200immediately upstream of the solenoid valve, are interconnected by meansof a channel 310 so that in both aforenoted spaces identical pressuresprevail. Further, the diameter of the cylindrical surface of armature28a sliding in the bore 24a in a fluidtight manner, is identical to thediameter of both seats for the sphere 22a. Thus, as long as the sphere22a is in a position shown in FIG. 4, the force derived from thepressure prevailing in bore 20a and exerted on the sphere in' theopening direction, is identical to the force of the pressurized liquidexerted on the sphere by the armature 28a in the closing direction.Spring 27a aids the latter force so that the sphere 22a is, as a netresult of the opposing forces, urged against the mouth or valve seatprovided about the bore 20a.

As soon as the coil 33a of the electromagnet is energized, for example,by an electronic control device, the force of the spring 27a is overcomeby the magnetic force and the armature 28a is displaced towards theleft. The pressurized liquid thus may flow through bore 20a, pressingthe sphere 22a against its other, opposite seat formed about the openingof bore 24a. As a result, sphere 22a closes the bore 24a so that theliquid ad mitted under pressure through the bore 23a may flow into thechamber 11a, displacing the actuating piston 9a. This results in theopening of the tappet valve 2a.

As soon as the solenoid 33a is de-energized, the spring 27a returns thearmature 28a and the sphere 22a into their initial position in which thebore 20a is again closed. As the bore 24a is opened by the returningsphere 22a, the liquid may flow from the chamber 11a through the bore24a, the channels 25a and 26a and the return conduit 26a to the suctionside of pump 14a allowing the actuating piston 9a to return. This, inturn, causes the tappet valve 2a to assume its closed position.

In the suction conduit 12a upstream of the return conduit 26'a there isdisposed a check valve 36a, so that the returning liquid generates apressure build-up at the suction side of the pump 14a resulting in animproved efficiency and power thereof.

In the embodiment shown. in FIGS. 4 and 5, the motion of the actuatingpiston 9a is hydraulically braked towards the end of each stroke. Forthis purpose, on the lateral surface of the actuating piston 9a there isprovided a collar 34a which, towards the end of the strokes of actuatingpiston 9a penetrates into one or the other cavity 35a, 35'a which haveapproximately the same diameter as the collar 340. As soon as the latterpenetrates into one of the cavities 35a, 35'a, it displaces the liquidpresent in that cavity through a radial throttle gap which is defined bythe wall of the cavity and the periphery of collar 34a. In this manner adampening of the motion of work piston 9a is achieved. To obtain agradual dampening effect, the walls of cavities 35a and 35 'a, as wellas collar 34a, may have a conical configuration.

In order to ensure that the solenoid valve operates with the requiredswitching speed at high engine rpms, the stroke of the armature 28a, aswell as the traveling path of the sphere 22a, is very small.Accordingly, the

flow passage sections of the solenoid valve are also small. In largerengines this would result in an excessive throttle effect. To avoid sucha disadvantage, according to this embodiment, the return and supplyconduits circumvent the solenoid valve and, controlled by a plunger 37a,lead directly to the chamber 11a. The

plunger 37a has a circumferential annular groove 38a I which is incontinuous communication with the supply channel 190 and an annularcircumferential groove 39a which, in turn, is in continuouscommunication with the return channel 26a. Depending upon the positionof the plunger 37a, one of the circumferential annular grooves 38a or390 communicates with a channel 40a which, in turn, when the tappetvalve 2a is in an open position, communicates with the chamber 11a. Theconnection between channel 40a and chamber 11a is controlled by theactuating piston 9a. Only after the latter has traveled a predeterminedpath, does the channel 40a open. For an axial pressure relief of thepiston 9a, the latter has, in the range of the mouth of channel 40a, acircumferential annular groove 41a.

When the solenoid valve 8a opens the channel 200 and the actuatingpiston 9a, urged by the force of the inflowing liquid, has traveled apredetermined path, communication is established between the channel 400and chamber 11a. Upon this occurrence, liquid may flow in an unthrottledmanner into the chamber Ila from channel 40a and the actuating pistonmay be displaced rapidly. As soon as the solenoid valve 8a is switched(i.e. de-energized), the liquid, driven partly by the returning piston9a and partly by the pump 14a through the channel 40a, flows through thebore 24a into the channel 25a and therefrom to the suction side of pump14a. In the channel 25a there is disposed a throttle 43a which causes abuild-up of the liquid upstream thereof.

The control plunger 37a operates in a bore 44a which is connectedthrough a channel 45a with the channel 25a upstream of the throttle 43a.As soon as said liquid buildup occurs in the channel 25a, by virtue ofthe throttle 43a, liquid flows under pressure through channel 45a intothe bore 44a and displaces the control plunger 37a against the force ofa spring 46a until said plunger abuts against a shoulder 47a of the bore44a (FIG. 5). Upon the aforenoted travel of the control plunger 37a, thesupply channel 19a is separated from the channel 40a, whereas throughgroove 39a, the return channel 26a is connected with the channel 40a. Asa result, the liquid may flow in an unthrottled manner from the chamber11a through the bore 40a, the annular groove 39a, the return channel 26aand the return conduit 26a to the suction side of the pump 14a.

Shortly before the tappet valve 2a closes, the actuating piston 9a shutsoff the channel 40a. During the entire period of the return motion ofactuating piston 9a, effected by the valve spring 6a, in the channel25a, there prevails a pressure (caused by the throttle 43a) which issufficient to maintain the control plunger 37a in its terminal positionshown in FIG. 5. As soon as the actuating piston 90, however, returnsinto its initial position, the liquid pressure in the channel 25adecreases, so that the spring 46a may return the control plunger 37ainto its initial position in which, as shown in FIG. 4, the supplychannel 19a is in communication with the channel 40a.

DESCRIPTION OF THE EMBODIMENT SHOWN IN FIGS. 6 AND 7 Turning now toFIGS. 6 and 7, the embodiment no play or clearance between the valvestem 3a and the actuating piston 9a.

For the aforenoted hydraulic operation, the control plunger 37a isprovided with a further annular circumferential groove 49a which, bymeans of radial bores a and an axial bore 51a, is connected with theannular circumferential groove 39a. For the hydraulic actuation of thepiston 9a the latter is provided with a collar 52a which is slidable ina fluidtight manner in a bore 530. From one end of the bore 53a thereextends a channel 48a which, dependent upon the position of the plunger37a, connects said end of bore 53a either with groove 49a (FIG. 6) orwith groove 38a (FIG. 7) of the plunger 37a. The other end of the bore53b is in continuous communication with the annular circumferentialgroove 390 through a channel 540. Instead of a throttle 43a in thechannel25a, there is provided, in this embodiment, in the return conduit26'a, a check valve 56a the opening pressure of which is designed insuch a manner that in the entire return channel system a sufficientlyhigh pressure is generated and maintained. As shown in FIG. 7, as soonas the control plunger 37a is displaced into its extreme position, thesupply channel 19a is in hydraulic communication with the channel 48athrough the annular circumferential groove 38a, so that the radial faceof the collar 52a of the piston 90 is exposed to a pressure in theclosing DESCRIPTION OF THE EMBODIMENT SHOWN IN FIGS. 8 AND 9 Turning nowto the embodiment shown in FIGS. 8 and 9, in a partially shown cylinderhead lb of an inter nal combustion engine there operates a tappet valve2b having a valve stem 3b axially slidably guided by a bearing sleeve 4bsecured in the wall of the cylinder head lb. The outer end of the valvestem 3b carries a spring seat disc 5b. Between the upper face of thecylinder head lb and the spring seat disc 5b there is disposed in apreloaded condition a valve closing spring 6b. To the cylinder head 1bthere is secured a housing bracket 7b containing a solenoid valvegenerally indicated at 8b and an actuating piston 9b. The latter isaxially displaceably guided in a fluid-tight manner in a bushing 10bsecured to the bracket 7b. During the valve movement, the lower terminalface of the actuating piston 9b is urged into contact with the valvestem 3b. The upper end of actuating piston 9b projects into a chamber11b.

A delivery pump 14b draws liquid from a tank 13b and delivers it under apressure of, for example 100 kg/cm, through a pressure conduit 15btowards the solenoid valve 8b. From the conduit 15b there extends,

downstreamjof the pump 14b, a return conduit 16b in which thereisdisposed a pressure control valve 17b and which terminates in the tank13b.

From conduit 15b there extend conduits 18b which lead to the controldevices of the other engine valves and which carry liquid under pressuredelivered by the same pump 14b.

In the bracket housing 7b supporting the solenoid valve 8b, the liquidfirst flows into a bore 20b which is connected with a control chamber21b. The mouth of the bore 20b at the control chamber 21b serves as a 10valve seat for a sphere 22b which is movably disposed in the controlchamber 21b. From the control chamber 21b there extends a bore 23b tothe chamber 1 1b. From the control chamber 21b there also extends a bore24b which is in continuous communication with the tank 13b through adischarge channel 25b and a return conduit 26b. The mouth of the bore24b at the control chamber 21b serves as a valve seat for the valvesphere 22b. An armature 28b, having a pin-like extension 28'b in contactwith the sphere 22b, is slidably disposed in the bore 24b and urges,under the action of a spring 27b, the sphere 22b into a position. inwhich it closes the bore 20b.

The control chamber 21b, the bore 24b and the armature 28b are containedin a valve support sleeve 29b which is inserted in the housing bracket7b and which is held in position by a flange of the housing 30b of theelectromagnet forming part of the solenoid 8b. The electromagnet chamberaccommodating the spring 27b and the bore 20b immediately upstream ofthe solenoid valve, are interconnected by means of a channel 31b so thatin both aforenoted spaces identical pressures prevail. Further, thediameter of the cylindrical surface of armature 28b sliding in the bore24b in a fluidtight manner, is identical to the diameter of both seatsfor the sphere 22b. Thus, as long as the sphere 22b is in a positionshown in FIG. 8, the force derived from the pressure prevailing in bore20b and exerted on the sphere in the opening direction, is identical tothe force of the pressurized liquid exerted on the sphere by thearmature 28b in the closing direction. Spring 27b aids the latter forceso that the sphere 22b is, as a net result of the opposing forces, urgedagainst the mouth or valve seat provided about the bore 20b.

As soon as the coil 33b of the electromagnet is energized, for example,by an electronic control'device, the force of the spring 27b is overcomeby the magnetic force and the armature 28b is displaced towards theleft. The pressurized liquid thus may flow through bore 20b, pressingthe sphere 22b against its other, opposite seat formed about the openingof bore 24b. As a result, sphere 22b closes the bore 24b so that theliquid admitted under pressure through the bore 23b may flow into thechamber 11b, displacing the actuating piston 9b. This results in theopening of the tappet valve 2b.

As soon as the solenoid 33b is de-energized, the spring 27b returns thearmature 28b and the sphere 22b into their initial position in which thebore 20b is again closed. As the bore 24b is opened by the returningsphere 22b, the liquid may flow from the chamber 11b through the bore24b, the channel 25b and the return conduit 26b to the liquid tank 13ballowing the actuating piston 9b to return. This, in turn, causes thetappet valve 2b to assume its closed position.

The aforenoted return motion of actuating piston 9b is, similarly to thethird embodiment hydraulically braked towards the end of its stroke.Thus, for this purpose, the lateral face of the work piston 9b isprovided with a collar 34b which, at the end of each return stroke ofpiston 9b, penetrates into a cavity 35b which has a diameterapproximately identical to that of the collar 34b. From the cavity 35bthe piston 9b displaces the liquid through a radial throttle gap formedbetween the wall of the cavity 35b and the periphery of the collar 34b.During the opening stroke of the tappet valve 2b, the collar 34b opens abore 36b through which lubricating oil may flow from a lubricatingsystem (not shown) into the cavity 35b. When subsequently, as shown inFIG. 9, the collar 34b emerges from the cavity 35b, the lubricating oilmay flow into the spring chamber of the tappet valve 217.

The throttle gap defined between the collar 34b and the cavity 35bnarrows towards the end of the return stroke in such a manner that apredetermined minimum volume remains locked between the collar 34b andthe cavity 35b. Said minimum volume, by means of its elasticity,functions as an equalizer of clearance between the actuating piston 9band the valve stem 3b. Such an equalization is advantageous since thedimensions of the valve stem 3b and the piston 9b vary as thetemperature changes.

DESCRIPTION OF THE EMBODIMENT ACCORDING TO FIGS. AND 1 1 Turning now tothe embodiment shown in FIGS. 10 and 11, similarly to theafore-described embodiments, in an only partially shown cylinder head 1cofan internal combustion engine there operates a tappet valve 20 havinga valve stem-3c axially slidably guided by a bearing sleeve 4c securedin the wall of the cylinder head 1c. The outer end of the valve stem 30carries a spring seat disc 50. Between the upper face of the cylinderhead 16 and the spring seat disc 5c there is disposed in a preloadedcondition a valve closing spring 6c. To the cylinder head It there issecured a housing bracket 7c containing a solenoid valve generallyindicated at 8c and an actuating piston 9c. The latter is axiallydisplaceably guided in a fluid-tight manner in a bushing 100 secured tothe bracket 7c. During the valve movement, the lower terminal'face ofthe actuating piston 96 is urged into contact with the valve stem 3c.The upper end of actuating piston 90 projects into a chamber 11c.

A delivery pump 14c draws liquid from a tank 13c and delivers it under apressure of, for example 100 kg/cm through a pressure conduit 15ctowardsthe solenoid valve 8c. From the conduit 15c there extends,downstream of the pump 140, a return conduit 160 in which there isdisposed a pressure control valve 17c and which terminates in the tank13c.

From conduit 150 there extend conduits 180 which lead to the controldevices of the other engine valves and which carry liquid under pressuredelivered by the same pump 140.

In the bracket housing 70 supporting the solenoid valve 80, the liquidfirst flows through a nipple 190 which is connected with a controlchamber 210 by means of a bore 20c. The mouth of the bore 200 at thecontrol chamber 21c serves as a valve seat for a sphere 22c which ismovably disposed in the control chamber 210. From the control chamber21c there extends a bore 230 to the chamber 11c. From the controlchamber 210 there also extends a bore 240 which is in continuouscommunication with the tank 130 through a discharge channel 256 and areturn conduit 260. The mouth of the bore 240 at the control chamber 21cserves as a valve seat for the valve sphere 220. An armature 28c, havinga pin-like extension 28's in contact with the sphere 220, is slidablydisposed in the bore 24c and urges, under the action of a spring 270,the sphere 22c into a position in which it closes the bore 20c.

The control chamber 21c, the bore 240 and the armature 28c are containedin a valve support sleeve 29c which is inserted in the housing bracket70 and which is held in position by a flange of the housing 300 of theelectromagnet forming part of the solenoid 8c. The electromagnet chamberaccommodating the spring 270 and the bore 20c immediately upstream ofthe solenoid valve,are interconnected by means of a channel 31c so thatin both aforenoted spaces identical pressures prevail. Further, thediameter of the cylindrical surface of armature 28c sliding in bore 24cin a fluid-tight manner, is identical to the diameter of both seats forthe sphere 220. Thus, as long as the sphere 22c is in a position shownin FIG. 10, the force derived from the pressure prevailing in bore 200and exerted on the sphere inthe opening direction, is identical to theforce of the pressurized liquid exerted on the sphere by the armature280 in the closing direction. Spring 27c aids the latter force so thatthe sphere 220 is, as a net result of the opposing forces, urged againstthe mouth or valve seat provided about the bore 200.

As soon as the coil 33c of the electromagnet is energized, for example,by an electronic control device, the force of the spring 27c is overcomeby the magnetic force and the armature 28c is displaced towards theleft. The pressurized liquid thus may flow through bore 20c, pressingthe sphere 220 against its other, opposite seat formed about the openingof bore 24c. As a result, sphere 22c closes the bore 24c, so that theliquid admitted under pressure through the bore 23c may flow into thechamber 11c, displacing the actuating piston 9c. This results in theopening of the tappet valve 2c.

As soon as the solenoid 33c is de-energized, the spring 27creturns thearmature 28c and the sphere 220 into their initial position in which thebore 200 is again closed. As the bore 240 is opened by the returningsphere 220, the liquid may flow from the chamber through the bore 240,the channel 250 and the return conduit 26c to the liquid tank allowingthe actuating piston 90 to return. This, in turn, causes the tappetvalve 2c to assume its closed position.

The motion of the actuating piston 90 may be hydraulically brakedtowards the end of each stroke. For this purpose, at the lateralcylindrical face of the actuating piston 90 there is provided a collar340 which, towards the end of each stroke, penetrates into one or theother cavity 350, 35c, which have approximately the same diameter as thecollar 340. As soon as the latter penetrates into one of the cavities35c, 35's, it displaces the liquid present in that cavity through aradial throttle gap defined by the wall of the cavity and the peripheryof the collar 340.

The power of the delivery pump is variable by means of a setting device370 which may be formed of a hydraulic setting piston, but it may be anelectric setting motor or any other similar device. The setting device370 receives control signals from an electronic control apparatus 38cwhich converts data relating to actual conditions (particularlycharacteristics of the engine operation, such as the position of theaccelerator 400 or the position of the brake pedal, as well as thepressure in the hydraulic system which is applied to apparatus 380through a conduit 410) into a desired value for the power of the pump140. This value is then applied to the setting apparatus 37c. Thepurpose of varying the power of pump 140 is to alter the pressure of theliquid that cause actuating piston 9c and thus valve 2c to execute itsopening stroke. By varying said pressure, the amplitude of the openingstroke of the tappet valve 2c may be varied, because the equilibriumbetween the opposing forces of hydraulic pressure and valve spring 6coccurs at different positions of the tappet valve 2c as the hydraulicpressure is changed.

Turning to FIG. 10a, the electronic control apparatus 380 includes theregulator 38R and the converter 38F which is in the feed-back circuit tothe regulator 38R. In the simplest case the regulator 38R is designed asan amplifier, the output volume of which controls theelectromagnetically operating volume regulator of the pump 14c. So as toobtain the precise value as indicated by the accelerator 40c for theoutput pressure of the pump 140, the feed-back circuit 410 forms withthe converter 38F a closed pressure regulating circuit. The converter38F generates an electric signal from the pressure appearing at theoutput of the pump 140; the magnitude of said electric signal iscomparable to the output volume or control value of the accelerator.

Independently from the afore-described control of 25 the hydraulicpressure in conduit 15c, the control apparatus 380 may also serve toenergize and de-energize the solenoid valve SC for initiating theopening and closing of the tappet valve 2c and thus determine the timingof valve operation.

EXAMINATION OF VALVE LIFT CURVES OBTAINABLE BY THE EMBODIMENT ACCORDINGTO FIG. 10

The diagram shown in FIG. 11 illustrates the ad vantage of theembodiment shown in FIG. 10. In this diagram the stroke s of the tappetvalve 20 is shown as a function of the angle of rotation at of theengine cam shaft. The stroke s indicates the structurally possiblelargest stroke of the tappet valve. Thecurve I encloses an open timearea obtained in case the valve 20 executes an opening stroke of maximumamplitude. When the power of the pump 14c is lowered, then the amplitudeof the opening stroke drops to s The resulting valve lift curve IIencloses a smaller open time area. By changing the opening or closingmoments, as indicated by curve III, the open time area may be furtheraltered.

DESCRIPTION OF THE EMBODIMENT ACCORDING TO FIG. 12

Turning now to the embodiment shown in FIG. 12, in a partially showncylinder head 1d of an internal combustion engine there operates atappet valve 2d having a valve stem 3d axially slidably guided by abearing sleeve 4d secured in the wall of the cylinder head 1d. The outerend ofthe valve stem 3d carries a spring seat disc 5d. Between the upperface of the cylinder head Id and the spring seat disc 5d there isdisposed in a preloaded condition a valve closing spring 6d. To thecylinder head 1d there is secured a housing bracket 7d containing asolenoid valve generally indicated at 8d and an actuating piston 9d.'Thelatter is axially displaceably guided in a fluid-tight manner in abushing 10d secured to the bracket 7d. During the valve movement, thelower terminal face of the actuating piston 9d is urged into contactwith the valve stem 3d. The upper end of actuating piston 9d projectsinto a chamber 1 1d.

A delivery pump 14d draws liquid from a tank 13d and delivers it under apressure of, for example 100 kg/cm through a pressure conduit 15dtowards the solenoid valve 8d. From the conduit 15d there extends,downstream of the pump 14d, a return conduit 16d in which there isdisposed a pressure control valve 17d and which terminates in the tank13d.

From conduit 15d there extend conduits 18d which lead to the controldevices of the other engine valves and which carry liquid under pressuredelivered by the same pump 14d.

In the bracket housing 7d supporting the solenoid valve 8d, the liquidfirst flows into a bore 20d which is connected with a control chamber21d of the solenoid valve 8d. The mouth of the bore 20d at the controlchamber 21d serves as a valve seat for a sphere 22d which is movablydisposed in the control chamber 21d. From the control chamber 21d thereextends a bore 23d to the chamber 1 1d. From the control chamber 21dthere also extends a bore 24d which is in continuous communication withthe tank 13d through a discharge channel 25d and a return conduit 26d.The mouth of the bore 240! at the control chamber 21d serves as a valveseat for the valve sphere 22d. An armature 28d, having a pin-likeextension 28'd in contact with the sphere 22d, is slidably disposed inthe bore 24d and urges, under the action of a spring 27d, the sphere 22dinto a position in which it closes the bore 20d.

The control chamber 21d, the bore 24d and the armature 28d are containedin a valve support sleeve 29d which is inserted in the housing bracket7d and which is held in position by a flange of the housing 30d of theelectromagnet forming part of the solenoid 8d. The

electromagnet chamber accommodating the spring 27d and the bore 20dimmediately upstream of the solenoid valve, are interconnected by meansof a channel 31d so that in both aforenoted spaces identical pressuresprevail. Further, the diameter of the cylindrical surface of armature28d sliding in the bore 24d in a fluidtight manner, is identical to thediameter of both seats for the sphere 22d. Thus, as long as the sphere22d is in a position shown in FIG. 12, the force derived from thepressure prevailing in bore 20d and exerted on the sphere in the openingdirection, is identical to the force of the pressurized liquid exertedon the sphere by the armature 28d in the closing direction. Spring 27daids the latter force so that the sphere 22d is, as a net result of theopposing forces, urged against the mouth or valve seat provided aboutthe bore 20d.

As soon as the coil 32d of the electromagnet is energized by anelectronic control device 33d, the force of the spring 27d is overcomeby the magnetic force and the armature 28d is displaced towards theleftfThe pressurized liquid thus may flow through bore 20d, pressing thesphere 22d against its other, opposite seat formed about the opening ofbore 24d. As a result, sphere 22d closes the bore 24d, so that theliquid admitted under pressure through the bore 23d may flow into thechamber 11d, displacing the actuating piston 9d. This results in theopening of the tappet valve 2d.

As soon as the solenoid 32d is de-energized, the spring 27d returns thearmature 28a and the sphere 22d into their initial position in which thebore 20d is again closed. As the bore 24d is opened by the returningsphere 22d, the liquid may flow from the chamber 11d through the bore24d, the channel 25d and the return conduit 26d to the liquid tank 13dallowing the actuating piston 9d to return. This, in turn, causes thetappet valve 2d to assume its closed position. The flow resistance ofthe channels ensures an operation free from play between the actuatingpiston 9d and the valve stem 3d.

The closing motion of the actuating piston 9d is, towards the end ofeach stroke, hydraulically braked. For this purpose on the lateral faceof the piston 9d there is provided a collar 34d which, towards the endof each stroke, penetrates into one or the other cavity 35d, 35d, whichhave approximately the same diameter as the collar 34d. From thecavities 35d, 35d, the collar 34d displaces the liquid through anannular gap defined by the wall of the cavity and the periphery of thecollar, resulting in a dampening of the piston stroke. The throttle gaphas to be of such minimum dimension that even at high rpms, the tappetvalve 2d closes entirely. a

By means of the electronic control apparatus 33d which is connectedthrough a conductor 37d with the solenoid 32d of the electromagnet, themoment of opening and closing of the tappet valve 2d may be controlledindependently from one another. The desired values of magnitude set bythe electronic control apparatus 33d are determined from the evaluationof actual sensed data, particularly those relating to operationalmagnitudes of the e'ngine, such as the position of the accelerator (i.e.load), rpm, external pressure, engine temperature, etc. The signalsrelating to the sensed actual magnitudes are applied through conductors38d .to the electronic control apparatus 33d. Such input signal may bederived, for example, from the position of an accelerator pedal 39d,sensed by a device 40d not shown in detail. Further, from the electroniccontrol apparatus 33d, there extend conductors 41d to control devices(not shown) for the other engine valves. Such electronic controlapparatus 33d as mentioned is described in the German Pat. No. 1,100,377(Bendix).

EXAMINATION OF VALVE LIFT CURVES OBTAINABLE BY THE EMBODIMENT ACCORDINGTO FIG; 12

The diagram shown in FIG. 13 illustrates the advantages of theembodiment shown in FIG. 12. In this diagram the stroke s (ordinate) ofthe tappet valve is illustrated as a function of the angular position a(abscissa) of the engine crankshaft (KW). The valve lift curvesassociated with an exhaust valve and an intake valve are shown side byside. In the example illustrated, the opening stroke is constant and isdesignated with s Further, the maximum open period of the exhaust valveconstant opening and closing velocity of the tappet valves,these curvesI have a relatively flat slope. In order to obtain at the intake valve alarge open time area, for obtaining a maximum engine power, the two liftcurves I overlap, that is, the intake valve begins to open before theexhaust valve is completely closed. In this example, the angle ofoverlap is the same.

The curves II represent a valve operation with minimum rpm under fullload conditions. By virtue of the low rpm, the slope of the lift curvesII for the opening and closing strokes, is substantially steeper thanthat of the lift curves I. It is seen that the duration of the openingstroke expressed in a is shorter here because i of the lower rpm. Theresult is a greater open time area.

Because of the aforenoted larger open time area, an overlap of theexhaust valve curve with the intake valve curve is not necessary. Forthe intake valve, this results in a rapid and optimal filling with airand at the exhaust valve there is a correspondingly rapid expansion andwithdrawal of the combustion gases. Thus, for example, as it may beobserved from the diagram, the opening moment of the exhaust valve maybe the same under full load conditions for maximum rpm and minimum rpm,whereas the closing moment for maximum rpm occurs later (to causeoverlap) than in case of minimum rpm. For the intake valve the converseap plies.

The curves III correspond to the partial load range. Here, too, themoment of closing the exhaust valve and the moment of opening the intakevalve may be shifted with respect to one another. Dependent upon therpm, the positive or negative slop of the curve may vary. The valveoperation may be altered, on the one'hand, as a function of the loadand, on the other hand, as a function of the rpm. The said variations asa function of load and rpm are independent from one another, because onecurve shift is effected as a function of the accelerator position,whereas the other is dependent upon the engine rpm. For the intakevalve, this type of control has the significant advantage that the meanpressure or the torque substantially increases with decreasing rpm whichresults in a decrease of the fuel consumption in case of a continuousinjection and further results in the decrease of the pollutants in theexhaust gases. Thus, a substantial improvement of the engine operationand particularly a quiet run in the idling range is achieved.

Curve IV pertains to an exhaust valve and encloses a relatively smallarea, so that beyond a determined rpm a braking effect appears. Theopening or closing moment of the exhaust valve is varied as a functionof the position of the brake pedal and the engine rpm. Thus, the openperiod of the exhaust valve is variable as a function of the brake pedalposition; the open time area of the exhaust valve decreases as the brakepedal changes its position in the direction of increased braking effect.In this manner, the braking moment of the engine aids the mechanicalbraking by forcing the engine piston to perform increased work duringits exhaust stroke. Preferably, during the actuation of the brake pedal,the fuel admission is shut off, so that only air is compressed anddisplaced.

The load-and-rpm-dependent change of the opening and closing moments ofthe intake and exhaust valves may contribute, in either Otto or dieselengines, to additional power increases. Thus, for example, as indicatedby the inlet valve curve V, under full load con ditions at maximum rpm,the lift curve of the intake valve may much more substantially overlapthe exhaust valve curve I than does the inlet valve curve I.Consequently, the open time area of the intake valve is increased. Theportion corresponding to the opening course of the intake valve is, incurve V, as compared to curve I, shifted parallel in the direction ofthe exhaust valve curve. By virtue of this increase of the open timearea, the so-called smoke limit is increased and, in diesel engines, theuse of a compressor becomes unnecessary.

Advantages may be further achieved by shifting the beginning and theterminal moment of the valve opening with respect to the crankshaftangle as illustrated by curve VI. For the exhaust valve, this curve VI,which corresponds to the partial load range, appears duringthe brakingof the engine by means of the exhaust valve.

The variable overlap or separation of the valve opening also has aneffect on the course of combustion and thus, on the composition ofexhaust gases. It is noted that the CO, CH and NO components appearmostly in the low to middle load and rpm ranges.

The CO content is reduced by means-of an overlap which decreases withthe rpm, in that the residual gas quantities are decreased and a leanermixture adaptation is possible. In addition, a miss-free operation maybe achieved.

The CH content may be reduced in this range by a large overlap possiblycoordinated with the injection periods. Particularly in case of delayswhen coasting in gear, the CH content may be substantially decreased bya decrease or elimination of the overlap. This valve control may beeffective to such an extent that the heretofore necessary fuel shut-offdevice operative while coasting in gear, may be dispensed with. i

The NO content is lowered by reintroducing the exhaust gas into theintake suction system; the variable valve time overlap is insofaradvantageous since the metering device and shut-off apparatus of anextem al exhaust reintroducing system may be omitted.

DESCRIPTION OFTHE EMBODIMENT ACCORDING TO FIG. 14

In a partially shown cylinder head 1d of an internal combustion enginethere operates a tappet valve 2e having a valve stem 3e axially slidablyguided by a bearing sleeve 42 secured in the wall of the cylinder head12. The outer end of the valve stem 32 carries a spring seat disc 52.Between the upper face of the cylinder head 12 and the spring seat disc52 there is disposed in a preloaded condition a valve closing'spring 62.To the cylinder head 12 there is secured a housing bracket 72 containinga solenoid valve generally indicated at 82 anda hydraulically operatedactuating piston 9e. The latter is axially displaceably guided in afluid'tight manner in a bushing 102 secured to the bracket 7e. Duringthe valve movement, the lower terminal face of the actuating piston 9eis urged into contact with the valve stem 32. The upper end of actuatingpiston 92 projects into a chamber 112 which leads to solenoid valve 82.7

A delivery pump 142 draws liquid from a tank 132 and delivers it under apressure of, for example 100 kg/cm through a pressure conduit 152towards the solenoid valve 82. From the conduit 152 there extends,downstream of the pump 142, a return conduit 162 in which there isdisposed a pressure control valve 172 and which terminates in the tank132.

From conduit 152 there extend conduits 182 which lead to the controldevices of the other engine valves and which carry liquid under pressuredelivered by the same pump 142.

In the bracket housing 72 supporting the solenoid valve 82, the liquidfirst flows into abore 202 which is connected with a control chamber212. The mouth of the bore 202 at the control chamber 212 serves as avalve seat for a sphere 222 which is movably disposed in the controlchamber 212. From the control chamber 212 there extends a bore 232 tothe chamber 112. From the control chamber 212 there also extends a bore242 which is in continuous communication with the tank 132 through adischarge channel 252 and a return conduit 262. The mouth of 'the bore242 at the control chamber 212 serves as a valve seat for the valvesphere 222. An armature 28e, having a pin-like extension 282 in contactwith the sphere 222, is slidably disposed in the bore 242 and urges,under the action of a spring 272, the sphere 222 into a position inwhich it closes the bore 202.

The control chamber 212, the bore 242 and the armature 282 are containedin a valve support sleeve 292 which is inserted in the housing bracket7eand which is held in position by a flange of the housing 302 of theelectromagnet forming part of the solenoid 82. The electromagnet chamberaccommodating the spring 272 and the bore 202 immediately upstream ofthe solenoid valve, are interconnected by means of a channel 312 so thatin both aforenoted spaces identical pressures prevail. Further, thediameter of the cylindrical surface of armature 282 sliding in the bore242 in a fluid-tight manner, is identical to the diameter of both seatsfor the sphere 222. Thus, as long as the sphere 222 is in a positionshown in FIG. 14, the force derived from the pressure prevailing .inbore 202 and exerted on the sphere in the opening direction, isidentical to the force of the pressurized liquid exerted on the sphereby the armature 282 in the closing direction. Spring 27e aids thelatter'force so that the sphere 222 is, as a net result of the opposingforces, urged against the mouth or valve seat provided about the bore202.

As soon as the coil 332 of the electromagnet is energized, for example,by an electronic control device, the force of the spring 272 is overcomeby the magnetic force and the armature 282 is displaced towards theleft. The pressurized liquid thus may flow through bore 202, pressingthe sphere seat formed about the opening of bore 242. As a result,sphere 222 closes the bore 242, so that the liquid adinto the chamber112, displacing the actuating piston 92. This results in the opening ofthe tappet valve 2e.

As soon as the solenoid 332 is de-energized, the

spring 272 returns the armature 282 and the sphere 222 into theirinitial position in which the bore 202 is again closed. As the bore 242is opened by the returning sphere 222, the liquid may flow from thechamber 112 222 against its other, opposite

1. In a control device for hydraulically operated tappet valves of aninternal combustion engine, said device being of the type that includesa reciprocating actuating piston mechanically connected to an associatedtappet valve for periodically opening the latter against the force of avalve closing resilient means, the improvement comprising A. a sourcecontinuously supplying pressurized hydraulic liquid, B. first channelmeans connecting said source with said actuating piston for deliveringpressurized hydraulic liquid to said actuating piston for exerting anopening force thereon, C. a hydraulic servo means having
 1. ahydraulically operated valve situated in said first channel means andadapted to assume a first position in which it blocks delivery of saidpressurized hydraulic liquid to said actuating piston and a secondposition for maintaining direct hydraulic communication between saidsource and said actuating piston for allowing delivery of saidpressurized hydraulic liquid to said actuating piston,
 2. means forurging said hydraulically operated valve into said first position, 3.second channel means connecting said source with said hydraulicallyoperated valve for delivering pressurized hydraulic liquid to saidhydraulically operated valve for exerting a force thereon to move itinto said second position, said first channel means and said secondchannel means being connected in parallel between said source and saidhydraulically operated valve,
 4. a solenoid valve situated in saidsecond channel means and adapted to assume a first position in which itblocks delivery of said last-named pressurized hydraulic liquid to saidhydraulically operated valve and a second position in which it allowsdelivery of said last-named pressurized hydraulic liquid to saidhydraulically operated valve, said first channel means fullycircumventing said solenoid valve,
 5. means for urging said solenoidvalve into its first position and D. means for intermittently energizingsaid solenoid valve for moving it periodically into its second position.2. means for urging said hydraulically operated valve into said firstposition,
 3. second channel means connecting said source with saidhydraulically operated valve for delivering pressurized hydraulic liquidto said hydraulically operated valve for exerting a force thereon tomove it into said second position, said first channel means and saidsecond channel means being connected in parallel between said source andsaid hydraulically operated valve,
 4. a solenoid valve situated in saidsecond channel means and adapted to assume a first position in which itblocks delivery of said last-named pressurized hydraulic liquid to saidhydraulically operated valve and a second position in which it allowsdelivery of said last-named pressurized hydraulic liquid to saidhydraulically operated valve, said first channel means fullycircumventing said solenoid valve,
 5. means for urging said solenoidvalve into its first position and D. means for intermittently energizingsaid solenoid valve for moving it periodically into its second position.